1. Field of the Invention
This invention relates generally to flow sensors, and more particularly a method of regulating resistance in a discontinuous time hot-wire anemometer commonly employing a heated resistance wire to sense flow rate.
2. Description of the Prior Art
Numerous applications require measurement of air flow rates. Hot wire air flow sensors, or anemometers, for example, are commonly employed as air flow sensors in ventilators and similar equipment. The anemometer utilizes a wire resistor that forms one arm of a Wheatstone bridge circuit. The other arms of the bridge circuit contain other resistors, one or more of which may be variable. A power supply is connected across one pair of terminals of the bridge circuit and an indicator device is connected across the other pair of terminals of the bridge circuit. Energization of the bridge circuit passes a current through the wire resistor to increase its temperature and cause it to become a “hot wire.” The resistance of the wire resistor is proportional to its temperature. As the flow rate increases, the wire resistor is cooled, altering its resistance. The resultant resistance imbalance in the bridge circuit, as sensed via the indictor device, is an indication of the flow rate passing the hot wire resistor.
Modern applications of anemometers such as described herein before, require lower power than that generally required in well known prior art applications. Further, these well known anemometer applications are disadvantageous in that the required supply voltage applied to the bridge circuit is dependent upon the mass airflow output signal generated via the indicator device(s).
In view of the foregoing, it is highly desirable and advantageous to provide a technique for regulating resistance in a hot-wire anemometer such that the supply voltage is not dependent upon the mass airflow output signal. It would further be advantageous and beneficial if the technique reduced the operational supply voltage requirements.